The present invention relates to an impact-type printing head.
A conventional printing head of the so-called clapper type is provided with a plurality of printing levers in correspondence with a plurality of printing elements and a plurality of electromagnetic driving devices for driving the respective printing levers. Each of the printing heads is also provided with a return spring comprising a coil spring or a plate spring for returning each of the printing elements. Each of the printing elements is advanced for printing by a corresponding electromagnetic driving device and then retracted to a standby position.
In the above-mentioned prior art, each of the printing levers is rotated by applying a current to the coil of each of the electromagnetic driving devices until the movable yoke portion of the corresponding printing lever becomes attracted by and adheres to the core element of each electromagnetic driving device. After printing has been effected by each printing element, each printing lever is retracted by a spring force stored in the return spring. However, since each of the movable yoke portions adheres to the corresponding core element, a large recovery force is require to separate them, and it takes a large force for each printing lever to move backwardly against the force of attraction. It is also very difficult to exert a constant attractive force on all the printing levers because of such influences as production errors and so on, and thus it is very difficult to equalize the respective times required for backwardly moving all the printing levers, resulting in discrepancies in movement characteristics between the respective printing levers.
It is an object of the present invention to eliminate the state in which the movable yoke portion of each of the printing levers adheres to the corresponding core element and to ensure that each of the printing levers is rapidly returned with a small return force, as well as enabling the reduction of differences between the movements of the respective printing levers so as to obtain a relatively uniform return motion.